1. Field of the Invention
The present invention generally relates to a magnetic material usable in an inductive head performing a magnetic recording to such a magnetic recording medium as a hard disk, and, more particularly, to a soft magnetic film having not only a high saturation flux density but also a good soft magnetism and an anisotropic magnetic field, as well as a good thermal stability and a corrosion resistivity.
2. Description of the Related Art
As a magnetic recording medium has been provided with a higher recording density, a coercive force in a magnetic layer in the medium has been increasing. Therefore, a magnetic material of a recording inductive head used in a magnetic disk device is required to have a high saturation flux density so as to enhance a magnetic field for writing information (writing magnetic field). Conventionally, a plated permalloy, such as Ni80Co20 or Ni45Fe55, is widely used as a magnetic pole of the inductive head, and a saturation flux density Bs of the permalloy is approximately 1-1.6T (tesla).
Additionally, Japanese Laid-Open Patent Application No. 11-74122 (Japanese Patent No. 2821456) proposes a material for a magnetic pole by enhancing the saturation flux density Bs close to 2T in CoNiFe. Henceforth, however, a recording density is surely to be made still higher, thus it is expected that there will be still increasing needs for a magnetic-pole material having a even higher saturation flux density Bs.
By the way, iron-cobalt (Fexe2x80x94Co) alloys are generally known as materials having a high saturation flux density Bs. However, it is extremely difficult to achieve a soft magnetism with a composition that has a saturation flux density Bs exceeding 2T. For example, Japanese Laid-Open Patent Application No. 11-121232 discloses a technology which achieves soft magnetism in a state in which a microcrystalline phase comprising Co and other ferromagnetic 3d transition metals (Fe, Ni) exists in an amorphous phase composed mainly of various metallic elements (M) and oxygen (O).
This technology sets forth that equal to or more than 20 at % of nonmagnetic elements (the above-mentioned metallic elements (M) and oxygen (O)) need to be added so as to generate an amorphous phase to a certain extent. Conversely, however, in order to realize a saturation flux density Bs equal to or more than 2T, the addition of nonmagnetic elements needs to be restrained as much as possible.
Thus, it is extremely difficult to realize a soft magnetic material having a high saturation flux density Bs equal to or more than 2T.
Additionally, Japanese Laid-Open Patent Application No.9-115729 reports a soft magnetic material comprising a ceramic phase and a ferromagnetic hyperfine microcrystalline phase. However, it is also difficult to achieve a high saturation flux density Bs because the soft magnetic material that comprises the ceramic phase has a small magnetic moment.
Further, page 691 of the Journal of the Magnetics Society of Japan, vol. 24 (2000), discusses a Fexe2x80x94Coxe2x80x94Alxe2x80x94O film manufactured by applying a magnetic field in the formation thereof. According to this journal, with a composition having a sparse proportion of nonmagnetic elements of aluminum (Al) and oxygen (O) which are restricted to 10 at % and 12 at %, respectively, an anisotropic magnetic field Hk becomes zero so as to make it difficult to obtain a uniaxial magnetic anisotropy.
Further in addition, Japanese Laid-Open Patent Application No. 10-270246 reports on a soft magnetic film having an anisotropic magnetic field (Hk greater than 20 Oe), a resistivity (p greater than 50 xcexcxcexa9cm), and a saturation flux density (Bs greater than 1.6T). However, in order to enhance the resistivity equal to or more than 50 xcexcxcexa9cm, the content of nonmagnetic elements other than magnetic elements needs to be increased. Consequently, the saturation flux density Bs decreases, as described above; thus, it is difficult to achieve a high saturation flux density Bs exceeding 2T. Further, a moderate anisotropic magnetic field Hk cannot be obtained, either.
As heretofore described, it is extremely difficult to form a soft magnetic film having not only a high saturation flux density Bs as well as a high resistivity, but also an appropriate soft magnetism and a moderate anisotropic magnetic field Hk.
These strict conditions imposed on a soft magnetic film are a reflection of strict conditions imposed on a magnetic head used for recording. In other words, as a magnetic disk device is provided with a higher recording density, a magnetic recording head is required to have magnetic properties as described above.
A soft magnetic film is required to have a high saturation flux density Bs, as described above, so as to intensify a writing magnetic field to write to a magnetic recording medium, in accordance with a highly dense recording.
Additionally, this soft magnetic film is often formed as a magnetic yoke functioning as a magnetic path that leads a writing magnetic field generated by coils to a recording medium. This magnetic yoke is required to have a high resistivity. Accordingly, the soft magnetic film is required to have a high resistivity as a further condition.
However, in accordance with a recent remarkable increase in recording density, the width of an end portion of the yoke as a magnetic pole has been becoming submicron. With this shape in which the width of the end portion of the magnetic pole is equal to or thinner than the thickness of the outer layer, a loss due to an overcurrent becomes, an amount that can be ignored. Therefore, the resistivity does not have to be enhanced very much at the end portion for the yoke; rather, a saturation flux density Bs should be increased in the first place.
It is noted that, when the resistivity becomes low at the end portion of the yoke, a design change is possible so as to secure a high resistivity in the yoke as a whole.
Further, the recording inductive head is often formed as a complex magnetic head arranged with a reproducing head used for reading. A soft magnetic film used for recording in this complex magnetic head requires further considerations with respect to influences of temperatures in an annealing process in manufacturing steps thereof, in addition to the above-mentioned conditions.
Specifically, in forming the soft magnetic film used in the inductive head, considerations have to be made so as not to deteriorate properties of a magnetoresistive element used in the reproducing head. It is pointed out in general that, in forming the soft magnetic film used in the inductive head, annealing the soft magnetic film at a temperature exceeding 300xc2x0 C. deteriorates the magnetoresistive element of the reproducing head.
For that reason, it is preferred that the soft magnetic film used in the inductive head has a soft magnetism at the formation thereof, and is thermally stable under approximately 300xc2x0 C., or that the soft magnetic film has magnetic characteristics such that the soft magnetism is improved by being annealed at 300xc2x0 C. or lower.
Therefore, a soft magnetic film disclosed in Japanese Laid-Open Patent Application No. 5-148595 is inappropriate as a magnetic-pole material used in a writing (inductive) head combined with a GMR reading (reproducing) head, because the soft magnetic material is annealed at 500-700xc2x0 C. to improve a soft magnetism thereof, as a result of which a reading property thereof is deteriorated.
Additionally, a thin-film material used therein is composed of elements analogous with the elements mentioned in Japanese Laid-Open Patent Application No. 11-121232, in which a ferromagnetic microcrystalline phase and a surrounding amorphous phase inferably form a crystal structure. A conceivable reason why the soft magnetism is improved at high temperatures of 500-700xc2x0 C. as mentioned above is that a structural relaxation and a phase change do not occur unless an activation energy corresponding to these temperatures is applied to a metastable phase comprising the ferromagnetic microcrystalline phase and the amorphous phase.
As heretofore described, there are a lot of conflicting requirements for a soft magnetic film used in an inductive head, and it is extremely difficult to meet these requirements.
It is a general object of the present invention to provide an improved and useful soft magnetic material in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide a soft magnetic material having a high saturation flux density Bs and exhibiting a preferably soft magnetic property immediately after being deposited or after being annealed at a low temperature.
In order to achieve the above-mentioned objects, there is provided according to one aspect of the present invention a soft magnetic film comprising Fe, Co, a metallic element (M), and oxygen (O), the soft magnetic film being represented by a composition formula of (Fe1-aCoa)xMyOz,
wherein the metallic element (M) is one selected from a group consisting of Al, B, Ga, Si, Ge, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Rh, Ru, Ni, Pd and Pt,
the composition formula fulfills the following conditions:
a=0.05-0.65;
y=0.2-9 at %, z=1-12 at %, and y+z= less than 15 at %; and
x=(100xe2x88x92yxe2x88x92z) at %, and
a crystal structure is formed by having a bcc phase as a principal phase, the bcc phase having a crystal grain not exceeding 50 nm in diameter, and the bcc phase including a solid solution of the metallic element (M) and the oxygen (O).
Additionally, in the soft magnetic film according to the present invention, the metallic element (M) may be an alloy composed of at least two selected from the group.
According to the present invention, the soft magnetic film is mainly composed of FeCo, added with nonmagnetic elements including a metallic element (M) and O. When the amount of the nonmagnetic elements is made equal to or smaller than 15 at %, along with the foregoing conditions being fulfilled, the soft magnetic film has a high saturation flux density Bs exceeding 2.1T so as to preferably form a writing magnetic field in an inductive head.
Additionally, in the soft magnetic film according to the present invention, a uniaxial magnetic anisotropy may be provided upon a formation thereof.
Additionally, in the soft magnetic film according to the present invention, a coercive force may be decreased by being annealed at a temperature lower than 300xc2x0 C. after a formation thereof.
According to the present invention, the soft magnetic film can be formed to have a preferable anisotropic magnetic field Hk. In addition, the soft magnetic film is thermally stable immediately after being formed, or after being annealed at 300xc2x0 C. or lower. When annealed preferably, the coercive force decreases so as to improve the soft magnetism. The soft magnetic film is also excellent in corrosion resistance.
Additionally, the soft magnetic film according to the present invention may further comprise an anisotropic microstructure.
Additionally, in the soft magnetic film according to the present invention, the anisotropic microstructure may have a major axis shorter than 50 nm, and a minor axis shorter than the major axis.
According to the present invention, the soft magnetic film has an anisotropic microstructure so as to have the uniaxial magnetic anisotropy from the formation of the film.
Additionally, in the soft magnetic film according to the present invention, an electrical resistivity may be equal to or lower than 50 xcexcxcexa9cm.
According to the present invention, the soft magnetic film exhibits a saturation flux density Bs higher than any conventional soft magnetic film, but allows the resistivity to become lower than 50 xcexcxcexa9cm. In this respect, the soft magnetic film according to the present invention is different from a conventional soft magnetic film that has a saturation flux density decreased so as to gain a high resistivity.
Additionally, the soft magnetic film according to the present invention may further comprise a different magnetic film laminated on at least one of an upper surface and an under surface thereof so as to form a composite film structure.
According to the present invention, the soft magnetic film is not only used as a single layer, but also can be used as a preferable composite film having a magnetic film of a different type arranged on and/or under the soft magnetic film.
In order to achieve the above-mentioned objects, there is also provided according to another aspect of the present invention a magnetic recording head comprising:
a soft magnetic film used in one of a whole magnetic pole and an end of the magnetic pole near a gap, the soft magnetic film containing Fe, Co, a metallic element (M), and oxygen (O) and being represented by a composition formula of (Fe1-aCoa)xMyOz,
wherein the metallic element (M) is one selected from a group consisting of Al, B, Ga, Si, Ge, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Rh, Ru, Ni, Pd and Pt,
the composition formula fulfills the following conditions:
a=0.05-0.65;
y=0.2-9 at %, z=1-12 at %, and y+z= less than 15 at %; and
x=(100xe2x88x92yxe2x88x92z) at %, and
a crystal structure is formed by having a bcc phase as a principal phase, the bcc phase having a crystal grain not exceeding 50 nm in diameter, and the bcc phase including a solid solution of the metallic element (M) and the oxygen (O).
Additionally, in the magnetic recording head according to the present invention, the metallic element (M) may be an alloy composed of at least two selected from the group.
According to the present invention, magnetic information can be recorded on a magnetic recording medium with high density. That is, in a case where a sub-magnetic pole is provided at an end of a magnetic yoke, the whole sub-magnetic pole may be formed by the soft magnetic film, or an end of the sub-magnetic pole near a gap may be formed by the soft magnetic film.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.